1. Field of the Invention
This invention relates generally to telecommunications, and more particularly, to wireless communications.
2. Description of the Related Art
Many service providers or network operators provide data and/or voice communication services over networks. A mobile wireless device may be used to avail these data and/or voice communication services. The information and/or communications for such services may be transmitted across a wireless telecommunications system according to one or more protocols. A wireless telecommunications system typically includes a plurality of base stations distributed within an area to be serviced by a digital cellular network. A transmitter in a mobile wireless device may exchange data across an air interface with a receiver in a base station and vice versa.
To meet the needs of growing market for the data and/or voice communication services, the service providers or network operators manage a host of radio resources, such as pan-European Global System of Mobile Communications (GSM) and Code Division Multiple Access (CDMA) cellular networks. In operation, various users within the area, fixed or mobile, may access the wireless telecommunications system and, thus, other interconnected telecommunications systems, via one or more of the base stations.
As a user moves across a network service region, a mobile wireless device maintains communications with the wireless telecommunications system as the mobile wireless device passes through an area by communicating with one and then another base station. The mobile wireless device may communicate with the closest base station, the base station with the strongest signal, the base station with a capacity sufficient to accept communications, etc. For a mobile wireless device to discontinue communications with a first base station and begin communications with a second base station when providing data and/or voice communications, a process known as soft hand off (SHO) was developed in the CDMA and UMTS systems to have multiple connections in the region of overlapped coverage.
During a conversation, for example, a mobile wireless device or a mobile terminal or a Mobile Station (MS), such as User Equipment (UE) often changes a cell. This cell change or transfer procedure is generally called handover. To decide when a handover is necessary, the mobile wireless device and a base station makes certain measurements during the conversation. For example, a GSM network may broadcast the mobile wireless device a list of neighboring cells to be measured. The measurements may be sent by a channel to the base station and therefore also to a Radio Network Controller (RNC). The RNC connects the base station to a Core Network (CN). Using these measurements from the mobile wireless device, the RNC may determine a cell, among the neighboring cells, which could be used for an eventual handover.
For example, a term “C1” generally represents a cell selection criterion. Specifically, the C1 criterion also called a path loss criterion refers to a value crucial in an idle mode during the selection of a cell. The C1 criterion decides which cell should be used by the mobile wireless device in an idle mode. A cell may only be used by a mobile terminal if the C1 criterion is higher than 0. Although the cell selection described here applies to GSM systems, such a cell selection is equally useful in other systems, such as Universal Mobile Telecommunication System (UMTS) systems. The mobile wireless device in the idle mode (or a stand-by mode) always uses the cell with the highest C1. That is, a cell can be used then by a phone as a current cell, if its calculated C1 is larger than 0. The C1 criterion may be calculated as follows: C1=(RX−RXLEV_ACCESS_MIN−MAX ((MX_TXPWR_MAX_CCH−MS_MAX_TXPWR), 0)). The term RX refers to a current receipt level, the term RXLEV_ACCESS_MIN refers to a minimum access receipt level into a cell, the term MX_TXPWR_MAX_CCH refers to a maximum transmitting power a mobile wireless device may use when accessing this cell on a control channel (CCH), and the term MS_MAX_TXPWR refers to a maximum possible transmitting power of the mobile wireless device.
However, hazards arising from electromagnetic waves due to transmitting power of mobile wireless devices are not adequately addressed from a medical point of view. One way to achieve public acceptance and/or to minimize electromagnetic exposure is to operate wireless 3G and 4G telecommunications systems, such as third and forth generation (3G and 4G) telecommunications systems at a minimum power level. Thus, reduction of emission power of the base stations in wireless telecommunications systems and development of such radio resource management techniques that keep the emission power of the base stations at a minimum level is desirable.
Specifically, the base stations (i.e., Node Bs) in conventional Third Generation Partnership Project (3GPP) based UMTS networks operate at carrier frequencies of about 2000 MHz with a maximum transmit power of 43 dBm. About 10% of this power is continuously used for the transmission of a common pilot channel (CPICH), giving rise to permanent interference and radio emission. A reduction of the radiation density of base stations can be achieved by lowering the transmit power of the common pilot channel. This reduces the interference level throughout the entire network and therewith the power of all users as well. On the other hand, the common pilot channel is one of the key factors for guaranteeing radio coverage. A reduction of pilot power generally results in higher failure rates due to the loss of coverage. Thus, more base stations are required to ensure the coverage leading to much higher installation costs.
Another approach calls for employing UMTS in lower frequency bands, e.g. 900 MHz or 450 MHz. The lower frequency bands provide a relatively better radio propagation properties and path loss will be much lower. Thus, using lower frequencies generally leads to lower emission power of the CPICH and consequently decreases the radiation density of the base stations.
However, when diverse radio access networks, such as 3G and 4G mobile telecommunication systems with different frequency bands are collocated, management of radio resources becomes difficult. Especially, with regard to emission reduction of the base stations, common radio resource management algorithms for load balancing among many frequency bands are not available.
Handover algorithms are not specified in the 3GPP-UMTS standards. Based on standardized measurements, most handover algorithms are vendor-specific. In one UMTS-based realization of an inter-frequency handover algorithm, handover control is primarily focused on the maintenance of the quality requirements of services. Moreover, inter-frequency handover algorithms in UMTS networks choose a target cell with the highest Ec/Nt value on the CPICH among all monitored cells. But the highest Ec/Nt value on CPICH does not always map onto the channel with the best radio propagation condition or the lowest radio emission. The term Ec/Nt is the ratio of the received pilot power to the total interference. Interference in this case is defined as the sum of all received CDMA power from other sectors and the thermal noise. Regarding cell selection, corresponding algorithms specified in the 3GPP-UMTS standards are based on quality measurements.
One disadvantage of the cell selection and the inter-frequency handover algorithms set forth is that it is possible that a cell with worse Ec/Nt emits less power since base station locations may be different for different network layers. For the same reason, the value of Ec/Nt is not necessarily linked to a load condition of a cell. Furthermore, “power-optimized” assignment of users to macro cells using lower frequency bands and to micro cells using higher frequency bands depends on the location of the user and the load conditions of the cells. As a consequence, efficient allocation of users to a proper frequency band in multi-layer networks may not be achieved.
The present invention is directed to overcoming, or at least reducing, the effects of, one or more of the problems set forth above.